Recovery of krypton and xenon



May 12, 1936 J. SCHLITT 2,040,108,

RECOVERY OF KRYPTON AND XENON Filed April 11, 1935 70 3 EXCHA N667? 2AIR INVENTCR Jere 44 L. sew/1% I ATTORNEYS Patented May 12, 1936 PATENTOFFICE 2,040,108 RECOVERY or KRYPTON AND XENON Joseph L. Schlitt,Darien, Conn., assignor to Air Reduction Company, Incorporated, NewYork, N. Y., a corporation of New York Application April 11, 1935,Serial No. 15,799

, 4 Claims.

This invention relates to the separation of the rare gases krypton andxenon from the atmosphere and the recovery of these gases in quan-' tonand xenon, and the ordinary methods of separating air for the recoveryof nitrogen, oxygen and argon take no account of the rarer gases.

No practicable method of recovering these gases has been availableheretofore, and consequently the gases have been used only forexperimental or scientific purposes.

It is the object of the present invention to provide a simple, practicaland efiective method of separating and recovering krypton and xenon fromthe atmosphere.

A further object of the invention is the provision of a method oftreating relatively tremendons volumes of air at a cost which permitsthe recovery and use of krypton and xenon for various commercial andindustrial purposes.

In carrying out the present invention, no attempt is made to recover allof the nitrogemoxy- 5 gen and argon as separate gases ofsubstantialpurity, since the primary function of the method is therecovery of the rarer gases krypton and xenon. Advantage is taken of theknown methods of separating the nitrogen and oxygen constituents of theatmosphere, but following the primary separation of these constituentsthey are utilized for the purpose of concentrating krypton and xenonfrom additional quantities of air. The

subsequent rectification of the liquids which ordinarily are rectifieddirectlyafter initial separation produces a liquid containingconsiderably greater proportions of krypton and xenon than are usuallypresent in the liquid product of the rectification. This liquid issubjected then to 40 a further rectification to effect separation ofoxygen, leaving a liquid concentrate rich in krypton and xenon which canbe withdrawn and utilized. A portion 'of the oxygen'and also of thenitrogen is also recoverable, but the major portion of all of the airtreated is returned to the atmosphere as a gaseous mixture from whichthe krypton and xenon has been removed.

The method as thus generally outlined will be better understoodbyreference to the follow- 50 mg specification and the accompanyingdiagram matic drawing, illustrating an apparatus which is adapted foruse in the practice of the method. It will be understood that details ofthe apparatus well known in the art are not illustrated 55 or described,the purpose being to present simtreated. The liquid flows backwardly andacply and clearly the essentials of the invention as hereinafterclaimed.

Referring to the drawing, a portion of the air to be treated, afterinitial compression to a suitable pressure and cooling in the usualexchang- 5 ers, is introduced through a pipe 5- to the bottomcompartment 6 of a column 1. The air passes upwardly through tubes 8immersed in a liquid product accumulated as hereinafter described, andthence downwardly through tubes 9 into a collector Hi. In passingthrough the tubes 8, the air is subjected to selective liquefaction withthe resulting formation of a liquid in phase equilibrium with thecomposition of the air, that is to say, a liquid containingapproximately from to of oxygen, the balance being nitrogen withsome ofthe argon and a considerable proportion of the krypton and xenon of theair cumulates in the compartment 6.

The unliquefied residue, consisting largely of nitrogen, in passingdownwardly through the tubes this also liquefied and accumulates in thecollector in. This liquid also may contain some 25 krypton and xenon aswell as a portion of the argon.

The two liquids which, in an ordinary air liquefaction system, areintroduced at separate levels in a rectification column to immediatelyeffect 30 a further separation of the constituents, are conductedinstead through pipes I and I2 to a column I3 having separatecompartments l4 and I5,

. each provided with the usual trays it, over which the liquids flow indirect contact with relatively 5 large volumes of air introduced througha pipe I! under pressure suificient only to ensure movement of the airthrough the apparatus. For

the purpose of moving the air, an ordinary blow- .er may be employed. 0

The air is introduced through the pipe I! to 4 the lower compartment l4and thence through a pipe l8 and valves l9 and 20 to the uppercompartment IS. The effect will be to wash from the large volume ofentering air, by means of the liquids introduced through the pipes IIand l2, substantially all of the krypton and xenon, together with someof the oxygen, while the effiuent from the upper compartment [5,escaping through the pipe 23, will consist of a gaseous 0 mixture,principally nitrogen, but containing oxygen and argon. The effluent maybe sent to an exchanger through a valve 24 and pipe 25, or deliveredthrough a pipe 26 for use as hereinafter described. The two liquids,enriched in krypton and nitrogen with some or .liquid and passes finallythrough xenon, which'accumulate in the bottom of of the compartments l4and I5, are withdrawn through pipes 2! and 28, controlledby valves 30and 3|, and are delivered to separate levels of the column 1 in whichthe usual rectification trays 29 are disposed.

In flowing downwardly over the trays 29, the two liquids introduced tothe column 1 are subjected to rectification with vapors arising from thebody of liquid surrounding the tubes 8 and 9. This liquid is vaporizedin the initial condensation of the entering air and the resultingvapors, together with those formed during the rectification,-passupwardly through the column 1 and escape as an efliuent, consistingprincipally of all of the argon present in the liquid, through a pipe33. The liquid flowing downwardly through the column finally accumulatesabout the tubes 8 and 9 and consists principally of oxygen withsubstantially all of the krypton and xenon which has been separated fromthe air entering through the pipes 5 and I 1.

A portion of the liquid, together with vapors from the lower part of thecolumn I, is delivered through pipes 34 and 35 controlled by valves 36and 31 to intermediate levels of an auxiliary column 38 containing theusual trays 39 and having at the bottom a coil 40 which is supplied withair previously compressed and cooled through a pipe 4|. In travelingthrough the coil, the air causes vaporization of the liquid surroundingthe coil and is itself liquefied and, it may be, somewhat subcooled; Theliquid travels through the pipe 42 and valve 32 to the chamber 6, thusjoining the liquid accumulating in that chamber. The vapor passesupwardly through the trays in contact with the downwardly flowing tubes43 of a condenser which is cooled by the efiluent escaping from'thecolumn 1, through the pipe ,33. A valve 44 controls'the flow of theeflluent which escapes finally through a pipe 45 to an exchanger. Byutilizing the pipe 26 a portion of the eflluent from the rectifier l3The condenser 43 separates from the vapors a liquid which becomes muchconcentrated in krypton and xenon when it reaches the bottom ofrectifier 38. The eflluent from this rectifier escapes through a pipe 46and consists of substantially pure oxygen which may be delivered throughan exchanger to a suitable collector in which the oxygen maybeaccumulated for use. The liquid at the bottom of the rectifier may bewithdrawn through a pipe 47. It consists of a concentrate of krypton andxenon and is the principal product of the method as described. It may beutilized after further purification for any desired purpose.

From the foregoing description it is very evident that the processforming the subject matter of this application is an efiicient andpracticable method of extracting the krypton and xenon from large bodiesof atmospheric air while at the same time an air separation apparatuseach for the production of high purity oxygen is operated in connectiontherewith. The relation between the air separation apparatus, which isof the well known Claude type, and the apparatus by means of whichkrypton and xenon are extracted from a large body of air not treated inthe air separation apparatus proper, is such thatan important advantageand economy in the air separation process itself is secured. This arisesfrom the fact that the two liquids intowhich the air entering the Claudecolumn is may be similarly utilized.

liquid fractions in order converted are enriched in oiwgen by reason oftheir passage through the krypton-xenon extractors 9 and I5. That is tosay, the two liquids entering the krypton-xenon extractors through pipes1 and I3 respectively and re-entering the Claude rectifier through pipes21 and 23 respectively both carry a higher percentage of oxygen afterleaving the krypton-xenon extractors than when they enter. Of course, aconsequence of this fact is that the effluent vapor leaving the 4 top ofthe krypton-xenon extractors contains a higher percentage air.

The method, as will be evident, afiords the possibility of treatinglarge quantities of air and the recovery therefrom in a simple andsatisfactory manner of the krypton and xenon content of the air,together with a separate portion consisting of oxygen in substantialpurity. Thus, krypton and xenon in quantities enabling the use of theseproducts for various commercial purposes are made available.

Various changes may be made in the details of the procedure andapparatus employed without departing from the invention or sacrificingany of the advantages thereof.

I claim:

of nitrogen than atmospheric 1. The method of separating and recoveringfractions each enriched in one of the major constituents of air, washingvolumes of air relatively said liquid fractions to produce liquidsenriched in krypton and xenon, rectifying the liquids with vaporsproduced therefrom and thereby accumu-' lating a liquid containingsubstantially all of the krypton and xenon from the air treated.

' 2. The method of separating and recovering krypton and xenon from theatmosphere which comprises, separating the air initially into liquidfractions each enriched in one of the major con stituents of air,washing volumes of air relatively large with respect to said liquidfractions with said liquid fractions to produce liquids enriched inkrypton and xenon, rectifying the liquids with vapors produced therefromand thereby accumulating a liquid containing substantially all of'thekrypton and xenon from the air treated, and subjecting the lastmentioned liquid to further rectification with vapors produced therefromto further concentrate the krypton and xenon by separating oxygentherefrom.

3. The method of separating and recovering oxygen, krypton and xenonfrom the atmosphere which comprises compressing a portion of the air tobe treated and separating this portion into two liquid fractions, one ofwhich is enriched in oxygen, krypton and xenon, and the other of whichis enriched in nitrogen, washing volumes of uncondensed, substantiallyuncompressed cold air which are relatively large with respect to said toenrich both liquids in krypton, xenon and oxygen, and thereafterrectifying the liquid resulting from the washing of said air to producea liquid containing substantially all the krypton and xenon contained inboth the compressed and uncompressed air and substantially more oxygenthan was contained in the primary compressed portion of the air.

4. The method of separating and recovering oxygen, krypton and xenonfrom the atmosphere large with respect to said liquid fractions with vwhich comprises compressing a portionof the air gen, krypton and xenon,and the other of which compressed anduncompressed air and substanisenriched in nitrogen, washing volumes of untially more oxygen than wascontained in the pricondensed, substantially uncompressed cold air marycompressed portion of the air, and. subject- I which are relativelylarge with respect to said liqing the last-mentioned liquid to furtherrectificauid fractions in order to enrich both liquids in tion withvapors produced therefrom to further krypton, xenon and oxygen,thereafter rectifyconcentrate the krypton and xenon and separate ing theliquid resulting from the washing of said oxygen therefrom. air toproduce a liquid containing substantially JOSEPH L. SCHLI'I'I. all thekrypton and xenon contained in both the i

